The present inventions relate generally to liquid crystal displays (LCDs). More specifically to methods and apparatuses for sealing LCD devices.
Today, small scale LCD devices, such as light valves are becoming more prominent. Small scale LCD devices, and light valves are typically manufactured according to certain specifications to ensure that they function properly. One criteria is that the pixel array is appropriately sealed to prevent contamination and ensure proper operation.
Referring to FIG. 1, a typical small scale LCD device 10 includes a die 20 containing a pixel array 22. Pixel array 22 is typically composed of rows and columns of electrically conductive pathways. At the intersection of a row and a column of the electrically conductive pathways is a pixel. Each pixel can be turned on individually by selecting the appropriate row and column of pixel array 22. Selection of a pixel is controlled by control circuitry, either included within the die 20 or external to the die 20. In both cases, external control signals may be used to control the functions of the die 20. Bond pads 25, are usually placed around pixel array 22, and typically connected to the pixel array 22 to allow control of the operation of the pixel array 22.
Bond pads 25 are electrically coupled to pixel array 22 by circuitry that is normally internal to the die 20. A glass plate 30 is typically placed over die 20 and pixel array 22, such that the glass plate 30 overhangs the die 20, and may cover an area of die 20 that could have contained bond pads 25. The placement of bond pads 25 are often concentrated to one or two sides of die 20, such that the glass plate 30 does not cover the bond pads 25.
Die 20 is typically mounted to a substrate 80. Substrate 80 includes a plurality of substrate pads 85. Bond pads 25 typically are wire bonded to the substrate pads 85 by bonding wires 90.
Typically, an adhesive seal 50 is formed between glass plate 30 and die 20 and surrounding pixel array 22. The sealed area between glass plate 30 and pixel array 22 is commonly filled with a solution of liquid crystal materials 60. After die 20 is properly affixed with glass plate 30, die 20 is attached and coupled to substrate 80, and sealed. Seal 50 contains the liquid crystal material 60 from leaking.
In typical LCD devices seal 50 often times does not maintain its integrity, which causes deformation and irregularities in the LCD devices. The failure of seal 50 to adequately adhere glass plate 30 to die 20 may cause artifacts 70. The artifacts may extend into the active area of the pixel array, causing visual aberrations in the final LCD device. Such artifacts render the LCD device defective.
FIGS. 2, 3 and 4 illustrate cross-sectional views of an LCD device 12. The cross-sections depict a glass plate 30 bonded to a die 20 by a seal 50. The interior is filled with liquid crystal material 60.
FIG. 2 illustrates the initial shape of seal 50 immediately after glass plate 30 is attached to die 20. Seal 50 sufficiently contains liquid crystal material 60. During the process of handling LCD device 12 many factors contribute to the deformation of seal 50, and LCD device 12 itself.
After glass plate 30 is attached to die 20 and LCD device 12 is filled with liquid crystal material 60 further processing steps require handling the LCD device 12. For example, the LCD device 12 is placed on a substrate (such as substrate 80 of FIG. 1). Also, LCD device 12 is subjected to functional testing. During these processing steps, LCD device 12 may undergo temperatures and stresses that may cause seal 50 to deform.
Referring to FIG. 3, many seals do not maintain their integrity during handling and/or testing of the LCD device. In typical LCD devices seal 50 is tensile. That is, seal 50 has a tendency to expand. The tensile nature of 50 becomes more troublesome during the heating and handling of the LCD device.
As illustrated, a common problem of the tensile nature of seal 50 is the delamination of liquid crystal material 60 from glass plate 30. Heating and/or handling of the LCD device may cause thermal excursion of the liquid crystal material. The liquid crystal material will typically tend to expand. Due to the tensile nature of seal 50, seal 50 may not contain the expanding liquid crystal material and expand outward, as illustrated. The liquid crystal material delaminates from the glass plate because the seal does not prevent the thermal excursion of the liquid crystal material.
A similar problem that causes artifacts in the LCD device is the deformation of the glass plate and/or the die. FIG. 4 illustrates a LCD device 12 with a deformed glass plate 30. Glass plate 30 (or die 20) may deform or bow during heating and/or handling of the LCD device. The deformation often times causes the glass plate to separate from the liquid crystal material 60. Again, seal 50 may not prevent the problem due to its tensile nature. The delamination of the glass plate from the liquid crystal material similarly causes artifacts in the LCD device that may render the device defective.
Therefore, current methods of sealing a LCD device may not sufficiently prevent delamination of the glass plate from the liquid crystal material. A seal that is capable of preventing the delamination of liquid crystal material from the glass plate is desired.
The present invention provides an improved seal for sealing a liquid crystal display (LCD) device. An improved seal is formed between a transparent plate and a die having a pixel array. The improved seal is configured to encircle the pixel array of the die when the die and the transparent plate are joined. The die and the transparent plate are joined together such that the improved seal is disposed between the transparent plate and the die.
In one embodiment, the improved seal is a hybrid seal. The hybrid seal includes a first seal encircling the pixel array of the die and adhesively coupling the transparent plate and the die. The hybrid seal further includes a second seal encircling the second seal.
In another embodiment, the first seal lacks a characteristic necessary for an effective seal. The second seal possesses the characteristic, such that the hybrid seal possesses the necessary characteristic.
These and other advantages of the present inventions will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.